The goal of Phase I is to prove the concept of a new biological microscope system design that will allow biologists to quickly visualize fine cell structures that extend in depth. This will ultimately lead to the creation of a commercial variable-depth 3D microscope (Phase II) whose features will provide biologists with advanced options for three-dimensional imaging of live-cell dynamics over time. In Phase I, the unique properties of a new family of optical elements will be investigated. These will be based on our wave front coding technology which has recently been used to produce a retrofit system that increases the depth of field of commercial fluorescence microscopes. In the first instance, pairs of the new optical elements will be mounted in a device so that one can be rotated with respect to the other. This will allow adjustment of the amount of increase in the depth of field. Perfecting this twin element rotating mount (TERM) will ultimately lead (in Phase II) to its insertion into a standard wide field microscope system that will allow biologists to dynamically control the depth of field while imaging live-cell processes. This new capability is important because it will allow biologists to quickly visualize fine cell structures that extend in depth and are therefore difficult to recognize using conventional wide field microscopes, where out-of-focus blur can mask features of interest along the Z axis. Similar difficulties arise in confocal-like (i.e. sectioning) microscopes where the initial optical section image may not reveal enough specimen information to cause the biologist to pause and acquire image stacks to build up an extended depth view. The proposed new TERM system carries added significance because it also provides the potential for recovering three-dimensional structural information without needing to change the focus position of the microscope. Incorporating this feature into our new microscope system will overcome a major drawback of other existing 3D microscope technologies (e.g. confocal, wide field deconvolution, multi-photon, and structured illumination) which lose valuable time acquiring images from multiple planes of focus when generating a 3D representation. An additional drawback to these multiimage- stack systems is that they often sacrifice signal (e.g. through photobleaching) or incur specimen photodamage due to the added exposure to light while acquiring multiple images.